The present invention relates to a power controller for mobile radio communication and, more particularly, to a power controller for controlling the RF (radio frequency) power of a an RF power amplifier such as a mobile telephone unit.
A conventional power controller includes a detector for extracting a part of a RF power output from a power amplifier and detecting the power, a power control unit for comparing the detection voltage with a predetermined reference voltage to control a feedback operation of the RF power output, and a digital/analog converter for generating the reference voltage in response to a digital signal output from an external circuit, thereby setting a target output power at a constant voltage.
In the above conventional power controller, a change in RF power caused by a change in control voltage of the power amplifier itself tends to be small at about 80 to 90% of a rated output and to be large at about 20 to 30% of the rated output, therefore, causing a large difference in sensitivity.
For this reason, in the digital/analog converter for outputting a reference voltage, its resolution must be increased to match a region having a high sensitivity. Since this resolution is kept unchanged in a region having a low sensitivity, bits are excessively used due to multi-stage power-down. In addition, a change in detection voltage output caused by a change in RF power passing through the detector is on the order of several hundreds mV at about 80 to 90% of the rated output, and the change in detection voltage output is on the order of several mV at about 20 to 30% of the rated output with the same rate of the RF power. For this reason, a difference in sensitivity occurs, and the same problem as described above is posed.